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Anything specific in logs? Please also try to change it too predefined component like promo (Remove Header). If that's work than issue is with Header component.
Try selecting Publish All Related Items. (Make sure all related items, including components, test variations, and layouts, are published from the master database to the web database.)
Check Sitecore logs and Right-click on your browser window and select Inspect or press F12, Network Tab, fill form again and check the request which got failed. Double confirm your end points (Domains and other urls)